Even if it doesn’t look like it on paper, this has been a big year for T-Mobile. Since January, the company has launched its LTE network, unveiled new plans, and has managed to get the attention of the larger carriers with its new ‘Jump‘ device upgrade program.

But perhaps the biggest thing that happened to T-Mobile this year was that it finally inked an iPhone deal. Until March, it was the only major US carrier not offering the handset. And according to a new study, landing it likely saved them over 300,000 customers…

The study comes from the Consumer Intelligence Research Partners (via Electronista), who conducted a poll with subscribers at T-Mobile prior to the iPhone launch. The results found that 25% of them were looking to jump ship before learning about the iPhone.

To be honest, I’m not quite sure where they get the 300,000 number. Their testing sample was small—like 500 people small—and it wasn’t defined. But I suppose they could have extrapolated their findings and applied them to T-Mobile’s churn over the last quarter.

Regardless, the data isn’t surprising considering that the carrier reportedly sold 500,000 iPhones in the handset’s first month, and nearly 1 million iPhones all together during the June quarter. A lot of folks were clearly awaiting the arrival of the popular smartphone.

The big takeaway here is that T-Mobile has found a way to keep a large number of its customers on board, which is a big deal for carriers. Add to that the 9 million or so new subscribers it’s gaining from its recent MetroPC acquisition, and things start to get interesting.